Cryogenic cable and process for making the same

ABSTRACT

A cryogenic cable including an internal cylindrical fluid-tight enclosure containing electrical conductors and carrying a cryogenic fluid. A thermal screen surrounds this enclosure, which is equipped with cooling conduits or ducts enveloped in the turned-out edges of the screen. An external enclosure surrounds the internal enclosure and the screen. The enclosures are formed by longitudinally folding a continuous metal strip and securing the edges which are then sealed by a welding joint. The construction thereof as well as that of the screen is performed at the place or location where the cable is to be laid.

United States Patent [191 Aupoix et al.

[ Mar. 27, 1973 CRYOGENIC CABLE AND PROCESS FOR MAKING THE SAME [75] Inventors: Marcel Aupoix, Paris; Francois Moisson-Franckhauser, Bretignysur-Orge, both of France [73] Assignees: Compagnie Generale DElectricite; LAir Liquide, Societe Anonyme Pour LEtude Et LExploitation Des Procedes Georges Claude, Paris, France 22 Filed: Mar. 6, 1972 21 Appl.No.: 232,163

[30] Foreign Application Priority Data Mar. 4, 1971 France ..7107527 [52] US. Cl. ..174/15 C, 174/27, 174/99 R, 174/DIG. 6

[51] Int. Cl. ..HOlv 11/00 [58] Field of Search ..174/15 C, 16 B, DIG. 6, 27, 174/28, 113 R, 126 R, 126 CP, 128, 1101- [56] References Cited UNITED STATES PATENTS 3,431,347 3/1969 Kaflta etal ..174/15 C 3,343,035 9/1967 Garwin ..174/15 C 3,512,581 5/1970 Lawton ....l74/15 C X 3,515,793 6/1970 Aupoix et ....l74/15 C X 3,529,071 9/1970 Kaflta ..174/15 C 3,595,982 7/1971 Kafka ..174/126 CP 3,600,498 8/1971 Aupoix ..174/15 C 3,604,832 9/1971 Kohler ..l74/l5 C 3,657,467 4/1972 Matthaus ..174/ 15 C Priniary Examiner-Bema.rd A. Gilheany Assistant ExaminerA. T. Grimley Attorney-Paul M. Craig, Jr. et al.

[ ABSTRACT A cryogenic cable including an internal cylindrical fluid-tight enclosure containing electrical conductors and carrying a cryogenic fluid. A thermal screen surrounds this enclosure, which is equipped with cooling conduits or ducts enveloped in the tumed-out edges of the screen. An external enclosure surrounds the internal enclosure and the screen. The enclosures are formed by longitudinally folding a continuous metal strip and securing the edges which are then sealed by a welding joint. The construction thereof as well as that of the screen is performed at the place or location where the cable is to be laid.

13 Claims, 7 Drawing Figures CRYOGENIC CABLE AND PROCESS FOR MAKING THE SAME The present invention relates to a generally cylindrical cryogenic cable construction of great length, as well as to a process for making the same.

It is known in the art to make cryogenic cables having a cylindrical shape and comprising generally an internal-enclosure which contains electrical conductors and in which a cryogenic fluid circulates. Disposed around this inner enclosure is a thermal screen, and an external enclosure surrounds both the inner enclosure and the thermal screen. The thermal screen is also generally equipped with cooling ducts or conduits.

For the purpose of making such cryogenic cables, the enclosures consist of ordinary metals, for example steel for the external enclosure and stainless steel for the internal enclosure, with the screen being generally made of copper or aluminum. Suspension systems are provided in order to maintain in place the internal enclosure and the screen within the external enclosure. The suspension systems of the internal enclosure and of the screen in the external enclosure must allow for the relative movements of the enclosures and of the screen which are due to the thermal contractions occurring when the unit is exposed to cold temperatures.

When using unit cable sections of great length (for example 400 meters), it is necessary to provide or plan for a process of formation of the sections that can be carried out in a simple manner since the geometric structure of this cable responds best to the circulation conditions of the cryogenic fluids and to the conditions of thermal insulation provided in the form of a vacuum. The geometric shape must be adapted to withstand the stresses which the cryolinkage undergoes. Presently existing cryogenic cables do not simultaneously meet all of these criteria. The formation and operation of the known arrangements is difficult; the thermal insulation formed by the vacuum is generally defective or insufficient; their formation at the location where they are to be set up can be made only in the form of sections having a short length; and their cost of manufacture and installation is therefore very high.

It is the object of the present invention to remedy these drawbacks; and therefore, the present invention makes it possible to form and install a cable of great length without any difficulty or great expense.

The present invention is directed to and concerned with a cryogenic cable comprising an internal cylindrical enclosure which is metallic and fluid-tight, this enclosure carrying a cryogenic fluid and containing a plurality of electrical conductors. A thermal screen is provided in surrounding relationship to the internal enclosure and is disposed at a distance therefrom; which cooling ducts are provided integral with this screen and an external cylindrical enclosure which is metallic and fluid-tight surrounds the screen at a distance therefrom. i

A system is provided for suspending the internal enclosure within the screen and for suspending the screen within the external enclosure. At least one perforated line or duct designed to produce a vacuum between the internal and external enclosures is provided in proximity to the screen and a thermal insulator occupies the space comprised between the screen and the external enclosure. Ducts for returning the cooling fluid from this screen are also disposed in this space, and ducts for returning the cooling fluid from the internal enclosure are disposed in the space comprised between the internal enclosure and the screen.

The present invention is particularly directed to the fact that this screen consists of a metallic strip which has been longitudinally bent into the form ofa cylinder, the two adjacent edges of this curved or bent band being partially bent down or flattened outwardly so as to include or envelope each one of these cooling ducts which are formed integral with the screen.

The cable of the present invention is further characterized by the fact that the aforementioned internal and external enclosures each consist of one continuous strip which has been longitudinally bent into the form of a cylinder, the two edges of this curved or bent strip being bent down or flattened out, one inwardly and the other outwardly with respect to the aforementioned cylinder, in such a manner as to form the edges into a U-shape. One U-shaped edge thus formed is hooked in the other U-shaped edge in such a manner as to provide for a clamping or clasping between the edges which forms a mechanical joint. The joint is then provided with a fluid-tight soldering or welding to form a tight seam.

The ducts which serve to return the cryogenic fluid cooling the screen (nitrogen, for example), which are disposed in the space between the screen and the external enclosure, are positioned in proper position between the screen and the external enclosure by means of thermally insulating spacer means arranged so as to support the screen within the aforementioned external enclosure. The ducts for returning the cooling fluid from the internal enclosure (this fluid being helium, for example) are also surrounded by or enclosed within thermally insulating spacer means.

The present invention is further directed to and concerned also with a process for making a cryogenic cable such as has been previously described, characterized in that it comprises a first operation subdivided into a first series of steps for preforming the external enclosure including the formation of the U-shaped edges of the aforementioned longitudinal mechanical connection of the seam, putting in place the means for maintaining the vacuum between the internal and external enclosure, and setting up the aforementioned ducts for returning the cooling fluid from the screen into the space comprised between this screen and the external enclosure, the return ducts being surrounded by or enclosed with the aforementioned thermally insulating spacer means. A second operation for preforming the thermal screen includes the steps of forming the edges of the screen so as to be outwardly bent or flattened out and setting up the ducts enveloped by the bent or flattened-out edges. A third operation for preforming the internal enclosure includes the formation of the aforementioned U-shaped edges of the longitudinal seam of the envelope and setting up the conductors in this enclosure. A fourth operation for closing the internal enclosure includes mechanically joining the U-shaped edges and forming the fluid-tight soldering of the seam. The next series of steps include putting in place the enclosure inside the preformed screen, setting up or putting in place the return ducts for the cooling fluid from the internal enclosure into the space comprised between the internal enclosure and the screen, these ducts being surrounded by or enclosed within thermally insulated spacer means for putting in place the means for suspending the internal enclosure and for closing the screen. The next operation is putting in place the preformed external enclosure the aforementioned internal enclosure suspended in the screen, and the final series of steps includes putting in place the suspension means for the screen, closing the external enclosure by joining the U-shaped edges thereof, and executing the fluid-tight soldering or welding of the joint.

One embodiment of a cryogenic cable as proposed by the present invention will now be described in detail purely as an example which is not to be considered as limiting, taken in connection with the accompanying schematic drawings, wherein FIG. 1 is a sectional view in perspective, arranged in layers, of a cable constructed according to the present invention, and

FIGS. 2 to 7 are schematic diagrams which illustrate various stages of the process for making the cable of FIG. 1.

The same elements have been identified with like reference numerals in the different figures. The cryogenic cable of FIG. 1 comprises an internal enclosurel consisting of a band or strip which has been bent or curved along its longitudinal axis in the form of a cylinder. This enclosure contains a plurality of electric conductors 40, the number of which has been limited to three by way of example for simplicity of description; however, it should be understood that more or less conductors could be provided.

In the central bore 50 of the conductors 40, which have been schematically shown in the form of tubes, a cryogenic fluid may circulate. A cryogenic fluid may also circulate around these conductors within the internal enclosure 10, the fluid-tightness of which is assured by means of the connection of U-shaped edges forming the seam 150 provided in the strip which has been shaped to provide this cylindrical enclosure. The aforementioned seam is further soldered or welded to provide a seal 160 for purposes of assuring the fluidtightness of the enclosure. I

The cryogenic cable of FIG. 1 further comprises a thermal screen which encloses the internal enclosure 10. This thermal screen has a cylindrical shape and may be made from strip aluminum, longitudinally bent or curved to shape and provided with perforations 170. The two edges of this bent strip are turned outwardly at 120 and 140 in a manner to locate and maintain in place ducts 110 and 130 for cooling this screen. The turned-out edges also may be punched out to provide transverse slots so as to constitute tongue portions which are then hard-soldered or brazed onto the ducts 110 and 130.

The internal enclosure containing the conductors is held coaxially with respect to the screen 20 by means of a suspension system formed by a wire connected to a horizontal plate 280, this plate being secured to a vertical plate 70, which in turn is soldered at to a rider portion 100, provided to keep in adjacent position the portions opposite the turned-out edges and of the screen. Cooling ducts or conduits 310 are disposed between the screen 20 and the internal enclosure 10. These conduits or ducts allow for the return of the cryogenic cooling fluid from the internal enclosure. They are surrounded in places by thermally insulating spacer means 320.

An external enclosure 30 is provided having the shape of a cylinder and is made from a bent or curved steel strip. The fluid-tightness of the enclosure is assured by the connection between the longitudinal edges of the strip and by means of the fluid-tight soldered or welded joint 190. Disposed in the space comprised between the screen 20 and the external enclosure 30 are means designed to produce the vacuum between the internal and the external enclosures. These means are schematically shown in FIG. 1 in the form of the suction tube 260 provided with perforations 270. It may be advantageous to surround or enclose this tube with a filtering packing or padding 250, such as felt.

A thermal insulating means 240 (for example a powder) fills the space comprised between the external enclosure 30 and the screen 20. In order to prevent the penetration of this powder into the space comprised between the internal enclosure 10 and the screen 20 through the perforations 170 of this screen, a band 250 made from filtering padding, such as felt, is wound around the screen.

Ducts or conduits 220 for the circulation of a cryogenic fluid are disposed in the space comprised between the screen 20 and the external enclosure 30. These conduits or ducts 220 assure the return of the cryogenic fluid which has been used for cooling the screen. Thermally insulating spacer means 230 are distributed in places over the length of the conduits or ducts 220 and effectively prevent these conduits or ducts from being accidentally displaced within the .interval or gap between screen 20 and external enclosure 30.

The suspension wire 90 assures the suspension of the screen 20 and the contents thereof in the external enclosure 30. The wire 90 is soldered at to this enclosure and is hooked in or clasped at its lower end by means of a lower support arrangement to an analogous system to that used to support internal enclosure 10, but separated from that support arrangement formed by plates 280, 70 and rider portion 100. The ducts or conduits 220 are advantageously placed within the lower portion of the space comprised between the screen 20 and the external enclosure 30. The insulating spacer means 230 being kept cold by the conduits or ducts 220 may constitute bearing supports between the thermal screen 20 and the external enclosure 30. The thermal losses or leaks in the screen produced by these supports are reduced by virtue of the fact that the major portion of the thermal flux in the insulating spacer means 210 and 230 is evacuated by the conduits or ducts, the temperature of which is not much higher than that of the thermal screen.

In the exemplary embodiment ofa cryogenic cable as proposed by the present invention, the supports of the thermal screen 20 consist of suspension wires 90. In case of a failure or breakdown of these supports, the screen rests on the spacer means 230; thus, the duplication of the system of supports is linked to an increased reliability. In case of a failure or breakdown of the supports 60 between the internal enclosure 10 and the screen 20, the internal enclosure will come to rest on the spacer means 320 surrounding the ducts or conduits 310. The spacer means 230 may consist, for example, of an insulating strip which is helically arranged around the tubes 220. I

The different stages of the process for making a cryogenic cable such as-proposed by the present invention will be described hereinafter. The first operation of this process comprises a first series of steps relating to the preform ation of the external enclosure 30. A steel strip wound on a reel or spool and having a width equal to the perimeter of the external enclosure 30 is preformed into cylindrical shape with the aid of an appropriate machine displaced on a gantry. The curvature which is given to this strip is a function of the final cylindrical shape of the enclosure. The U-shaped edges which will form the seam connection 180 are then formed. The suction or pumping duct 260 to be connected to the vacuum source and conduits 200, 220 are put in place, the duct 260 being equipped with perforations and the conduits 200 and 220 (FIG. 6) serving for the return of the cryogenic fluid. The spacer means 210 and 230 are also provided at this time. The preformed external enclosure is shown in FIG. 6.

This first operation also comprises a second series of steps relating to the preformation of the thermal screen 20, such as shown in FIG. 2. A strip of aluminum equipped with perforations 170 (shown in FIG. 1) is provided at the place for laying the cryogenic cable wound on a reel. The edges of this strip are punched to provide transverse slots and tongue portions. This strip which has a width equal to the perimeter of the screen 20 is then preformed with the aid of an appropriate machine which is displaced on the setting gantry. The preforming curvature of the screen is defined as a function of the final cylindrical shape to be obtained. The edges 120 and 140 of the strip are bent outwardly; and, the conduits or ducts 110 and 130 for cooling the screen are put in place. The edges 120 and 140 are then completely turned out in such a manner as to maintain the conduits or ducts in contact with the screen. A hard-soldering or brazing of these turned-out edges on the conduits or ducts is then carried out.

The first operation also comprises a third series of steps relating to preforming the internal enclosure 10 and putting in place the conductors 40 at the interior of this preformed enclosure in the manner illustrated in FIG. 3. A strip wound on a reel and having a width equal to the perimeter of the internal enclosure 10 is preformed with the aid of an appropriate machine. Its curvature is defined as a function of the final cylindrical shape which the enclosure 10 must have. With the aid of an appropriate machine, the U-shaped edges are then formed and the conductors 40 are disposed within the preformed enclosure 10.

Finally, this first operation comprises a fourth series of steps, illustrated in FIG. 4. The internal enclosure 10 is closed and the seam is formed by the mechanical connection 150. A fluid-tight solder or welded joint 160 is then provided for on this seam.

The second operation of the process for obtaining or making the cryogenic cable as proposed by the present invention is shown in FIG.-5. The internal enclosure 10 containing the conductors 50 and the suspension means 60, 70, 280 and 100 are put in place as well as the ducts or conduits 310 serving for the return of the cooling fluid from the internal enclosure. The screen 20 is 'closed so as to adopt its definitive cylindrical shape. Also closed at this time are the rider portions so as to maintain the turned-out edges and of this screen adjacent thereto. The packaging 250 is then wound on the cylindrical screen thus formed.

The third operation of the process is shown in FIG. 6. The system, consisting of the screen 20, the internal enclosure 10, the conductors 40 and the suspension means 60, 70, 280 and 100, is put in place in the preformed external enclosure 30, and the thermal insulating means (insulating powder) is disposed in the preformed external enclosure.

The fourth operation of the process is shown in FIG. 7. The external enclosure 30 is closed by joining the U- shaped edges to form the joint and the fluid-tight solder or weld is then applied. The supporting wire 90 which is part of the suspension means for the screen is soldered at 190.

The foregoing specific descriptions are directed to superconductive cryogenic cables. It is understood that cryoresistant linkages or connections (for example cables from refined aluminum cooled with liquid nitrogen) are inferred from the structure described herein upon deletion of the thermal screen without departing from the spirit and scope of the present invention.

What is claimed is:

1. A cryogenic cable comprising an inner cylindrical metallic fluid-tight enclosure containing a plurality of electrical conductors and carrying a cryogenic fluid, a thermal screen mounted in spaced surrounding relationship to said inner enclosure, a plurality of cooling conduits mounted integrally with said thermal screen, an outer cylindrical metallic fluid-tight enclosure mounted in spaced surrounding relationship to said thermal screen, support means for suspending the combination of said inner enclosure and said thermal screen within said outer enclosure, at least one perforated duct mounted adjacent said thermal screen within said outer enclosure for producing a vacuum between the inner and outer enclosures, thermal insulating means disposed in the space between said screen and said outer enclosure, a plurality of return cooling conduits disposed in the space between said screen and said outer enclosure and a plurality of additional return cooling conduits disposed in the space between said screen and said inner enclosure, said thermal screen being formed of a longitudinally curved metal band having the longitudinal edges thereof curved outwardly around said cooling conduits and in intimate contact therewith. I

2. A cryogenic cable as defined in claim 1 wherein said inner and outer enclosures are each formed of a longitudinally curved metal band having one longitudinal edge curved outwardly in a U-shape and the other longitudinal edge curved inwardly in a U-shape, the two U-shaped longitudinal edges being coupled to form a mechanical joint.

3. A cryogenic cable as defined in claim 2 wherein said mechanical joint is welded to render it fluid-tight.

4. A cryogenic cable as defined in claim 1 wherein said return cooling conduits and said additional return cooling conduits are enclosed in thermally insulating spacers.

5. A cryogenic cable as defined in claim 1 wherein said thermal screen is perforated over substantially its entire surface.

6. A cryogenic cable as defined in claim 1 wherein the longitudinal edges of said thermal screen are provided with spaced tongue portions which are formed around said cooling conduits and secured in intimate contact therewith.

7. A cryogenic cable as defined in claim 1 wherein said thermal insulating means includes a fibrous insulating strip wound about said thermal screen and an insulating powder disposed between said insulating strip and said outer enclosure.

8. A cryogenic cable as defined in claim 1 wherein said support means includes a cable connected between said outer enclosure and said shield.

9. A cryogenic cable as defined in claim 8 wherein said return cooling conduitsand said additional return cooling conduits are enclosed in thermally insulating spacers.

10. A cryogenic cable as defined in claim 9 wherein said return cooling conduits and said additional return cooling conduits with the respective insulating spacers have an outer diameter equal to the distance between said screen and said outer enclosure and between said screen and said innerenclosure, respectively.

11. A cryogenic cable as defined in claim 10 wherein said thermal screen is perforated over substantially its entire surface.

12. A cryogenic cable as defined in claim 11 wherein said thermal insulating means includes a fibrous insulating strip wound about said thermal screen and an insulating powder disposed between said insulating strip and said outer enclosure.

13. A cryogenic cable as defined in claim 12 wherein said inner and outer enclosures are each formed of a longitudinally curved metal band having one longitudinal edge curved outwardly in a U-shape and the other longitudinal edge curved inwardly in a U-shape, the two U-shaped longitudinal edges being coupled to form a mechanical joint. 

1. A cryogenic cable comprising an inner cylindrical metallic fluid-tight enclosure containing a plurality of electrical conductors and carrying a cryogenic fluid, a thermal screen mounted in spaced surrounding relationship to said inner enclosure, a plurality of cooling conduits mounted integrally with said thermal screen, an outer cylindrical metallic fluidtight enclosure mounted in spaced surrounding relationship to said thermal screen, support means for suspending the combination of said inner enclosure and said thermal screen within said outer enclosure, at least one perforated duct mounted adjacent said thermal screen within said outer enclosure for producing a vacuum between the inner and outer enclosures, thermal insulating means disposed in the space between said screen and said outer enclosure, a plurality of return cooling conduits disposed in the space between said screen and said outer enclosure and a plurality of additional return cooling conduits disposed in the space between said screen and said inner enclosure, said thermal screen being formed of a longitudinally curved metal band having the longitudinal edges thereof curved outwardly around said cooling conduits and in intimate contact therewith.
 2. A cryogenic cable as defined in claim 1 wherein said inner and outer enclosures are each formed of a longitudinally curved metal band having one longitudinal edge curved outwardly in a U-shape and the other longitudinal edge curved inwardly in a U-shape, the two U-shaped longitudinal edges being coupled to form a mechanical joint.
 3. A cryogenic cable as defined in claim 2 wherein said mechanical joint is welded to render it fluid-tight.
 4. A cryogenic cable as defined in claim 1 wherein said return cooling conduits and said additional return cooling conduits are enclosed in thermally insulating spacers.
 5. A cryogenic cable as defined in claim 1 wherein said thermal screen is perforated over substantially its entire surface.
 6. A cryogenic cable as defined in claim 1 wherein the longitudinal edges of said thermal screen are provided with spaced tongue portions which are formed around said cooling conduits and secured in intimate contact therewith.
 7. A cryogenic cable as defined in claim 1 wherein said thermal insulating means includes a fibrous insulating strip wound about said thermal screen and an insulating powder disposed between said insulating strip and said outer enclosure.
 8. A cryogenic cable as defined in claim 1 wherein said support means includes a cable connected between said outer enclosure and said shield.
 9. A cryogenic cable as defined in claim 8 wherein said return cooling conduits and said additional return cooling conduits are enclosed in thermally insulating spacers.
 10. A cryogenic cable as defined in claim 9 wherein said return cooling conduits and said additional return cooling conduits with the respective insulating spacers have an outer diameter equal to the distance between said screen and said outer enclosure and between said screen and said inner enclosure, respectively.
 11. A cryogenic cable as defined in claim 10 wherein said thermal screen is perforated over substantially its entire surface.
 12. A cryogenic cable as defined in claim 11 wherein said thermal insulating means includes a fibrous insulating strip wound about said thermal screen and an insulating powder disposed between said insulating strip and said outer enclosure.
 13. A cryogenic cable as defined in claim 12 wherein said inner and outer enclosures are each formed of a longitudinally curved metal band having one longitudinal edge curved outwardly in a U-shape and the other longitudinal edge curved inwardly in a U-shape, the two U-shaped longitudinal edges being coupled to form a mechanical joint. 